M. Vepsalainen

Heavy quarkonium in any channel in resummed hot QCD

We elaborate on the fact that quarkonium in hot QCD should not be thought of as a stationary bound state in a temperature-dependent real potential, but as a short-lived transient, with an exponentially decaying wave function. The reason is the existence of an imaginary part in the pertinent static potential, signalling the “disappearance”, due to inelastic scatterings with hard particles in the plasma, of the off-shell gluons that bind the quarks together. By

Quarkonium dissociation in the presence of a small momentum space anisotropy

We consider the dissociation of heavy quarkonium in a medium close to thermal equilibrium but with a small momentum space anisotropy. Dissociation is defined to take place when the width of the ground state equals its binding energy. We show that if the anisotropic medium is obtained isentropically from the equilibrium one, then to first order in the anisotropy parameter the dissociation temperature remains unchanged. If, in contrast, the non-equilibrium system has a smaller entropy density than the equilibrium one, then the dissociation temperature increases with respect to the isotropic case, by up to ∼ 10% for modest anisotropies.

Dimensionally regularized Polyakov loop correlators in hot QCD

A popular observable in finite-temperature lattice QCD is the so-called singlet quark-antiquark free energy, conventionally defined in Coulomb gauge. In an effort to interpret the existing numerical data on this observable, we compute it at order

Mesonic correlation lengths in high temperature QCD

\mathcal{O}\left( {\alpha_s^2} \right)

Ultraviolet asymptotics of scalar and pseudoscalar correlators in hot Yang-Mills theory

in continuum, and analyze the result at various distance scales. At short distances (r ≪ 1/πT) the behaviour matches that of the gauge-independent zero-temperature potential; on the other hand at large distances (r ≫ 1/πT) the singlet free energy appears to have a gauge-fixing related power-law tail. At infinite distance the result again becomes physical in the sense that it goes over to a gauge-independent disconnected contribution, the square of the expectation value of the trace of the Polyakov loop; we recompute this quantity at

On the smallest screening masses in hot QCD

\mathcal{O}\left( {\alpha_s^2} \right)

Heavy quark medium polarization at next-to-leading order

, finding for pure SU(Nc) a different non-logarithmic term than in previous literature, and adding for full QCD the quark contribution. We also discuss the value of the singlet free energy in a general covariant gauge, as well as the behaviour of the cyclic Wilson loop that is obtained if the singlet free energy is made gauge-independent by inserting straight spacelike Wilson lines into the observable. Comparisons with lattice data are carried out where possible.

Frequency and wave number dependence of the shear correlator in strongly coupled hot Yang-Mills theory

We consider spatial correlation lengths xi for various QCD light quark bilinears, at temperatures above a few hundred MeV. Some of the correlation lengths (such as that related to baryon density) coincide with what has been measured earlier on from glueball-like states; others do not couple to glueballs, and have a well-known perturbative leading-order expression as well as a computable next-to-leading-order correction. We determine the latter following analogies with the NRQCD effective theory, used for the study of heavy quarkonia at zero temperature: we find (for the quenched case) xi(-1) = 2piT + 0.1408g(2)T, and compare with lattice results. One manifestation of U-A(1) symmetry non-restoration is also pointed out.

Pressure of the standard model at high temperatures

Inspired by recent lattice measurements, we determine the short-distance (a ≪ r ≪ 1/ πT) as well as large-frequency (1/a ≫ ω ≫ πT) asymptotics of scalar (trace anomaly) and pseudoscalar (topological charge density) correlators at 2-loop order in hot Yang-Mills theory. The results are expressed in the form of an Operator Product Expansion. We confirm and refine the determination of a number of Wilson coefficients; however some discrepancies with recent literature are detected as well, and employing the correct values might help, on the qualitative level, to understand some of the features observed in the lattice measurements. On the other hand, the Wilson coefficients show slow convergence and it appears uncertain whether this approach can lead to quantitative comparisons with lattice data. Nevertheless, as we outline, our general results might serve as theoretical starting points for a number of perhaps phenomenologically more successful lines of investigation.

The Ultraviolet limit and sum rule for the shear correlator in hot Yang-Mills theory

The heavy ion event generator HYDJET++ is presented. HYDJET++ simulates relativistic heavy ion AA collisions as a superposition of the soft, hydro-type state and the hard state resulting from multi-parton fragmentation. This model is the development and continuation of HYDJET event generator. The hard parts of HYDJET and HYDJET++ are identical. The soft part of HYDJET++ contains the following important additional features as compared with HYDJET: resonance decays and more detailed treatment of thermal and chemical freeze-out hypersurfaces. HYDJET++ is capable of reproducing the bulk properties of heavy ion collisions at RHIC (hadron spectra and ratios, radial and elliptic flow, femtoscopic momentum correlations), as well as high-pT hadron spectra. Some applications of HYDJET++ at LHC are discussed.The heavy ion event generator HYDJET++ is presented. HYDJET++ simulates relativistic heavy ion AA collisions as a superposition of the soft, hydro-type state and the hard state resulting from multi-parton fragmentation. This model is the development and continuation of HYDJET event generator. The hard parts of HYDJET and HYDJET++ are identical. The soft part of HYDJET++ contains the following important additional features as compared with HYDJET: resonance decays and more detailed treatment of thermal and chemical freeze-out hypersurfaces. HYDJET++ is capable of reproducing the bulk properties of heavy ion collisions at RHIC (hadron spectra and ratios, radial and elliptic flow, femtoscopic momentum correlations), as well as high-pT hadron spectra. Some applications of HYDJET++ at LHC are discussed.The increasing focus on unquenched lattice simulations has revived interest also in gluonic screening masses, whose inverses characterise the longest length scales at which thermal fluctuations are correlated in a hot non-Abelian plasma. We fill an apparent gap in the literature concerning the theoretical structure of one of the relevant screening masses (the one which equals twice the Debye mass at leading order), by showing that the next-to-leading order correction to it is perturbative and small. This surprising result appears to explain semi-quantitatively why this particular channel yields the smallest gluonic screening mass at temperatures around a few hundred MeV (it couples to the energy density and to the real part of the Polyakov loop), even though it is not among the smallest screening masses at asymptotically high temperatures.